Pyro! Lots and lots of pyro. I've only played one night game so I'm by no means an expert on the subject. That said, the game I did play in had a designated guy setting off the fireworks all night. It's been my experience that most people can't see shit in the dark. Stands to reason, since humans weren't designed with the ocular abilities of cats and owls. So, you have to let people wandering around a large playing area in the dark know where the action is taking place. Having very clear objectives and a couple very responsible and saftey oriented people on each team setting off para flares and fireworks the whole time keeps the action tight for some people. For those who want the stealth and adrenaline of sneaking up on an enemy position in the dark. Well, now they will know where that position is. What with all the shadows, bright flares destroying yours, and their, night vision, you can still get right up to an enemy position before they know it.
So to precis: A) Very clear objectives. B) Lots shit that blows up and makes pretty colours. C) People who can be trusted to blow shit up and make pretty colours in a safe manner.
Like I said, I'm new to this so others might have a lot better information to offer. Good luck.